Japanese Patent Application Laid-Open No. H9-48630 discloses a method of manufacturing fluorine doped glass. In this method, a soot glass deposit body is put in a container, and fluorine compound gas is supplied into a container while heating the inside of the container so that fluorine is added to the soot glass deposit body. And, subsequently, the soot glass deposit body is consolidated into transparent glass. While fluorine is added to the soot glass deposit body, the concentration of fluoric raw material in the container is controlled to be 4% by volume. Japanese Patent Application Laid-Open No. S62-230638 discloses a method in which, when a fine glass particles deposited body is subjected to a heat treatment in an atmosphere which includes a fluorine compound, the partial pressure of the fluorine compound is changed. In this method, the partial pressure of the fluorine compound is changed according to the variation of the temperature.
In the methods disclosed in these documents, most of the fluorine compounds are exhausted, simply passing through the container. Therefore, the ratio (yield) of the amount of the fluorine added to the soot glass deposit body relative to the amount of the fluorine supplied into the container is very small, which has resulted in the waste of most of the expensive fluorine compounds.
Patent document 1: Japanese Patent Application Laid-Open No. H9-48630
Patent document 1: Japanese Patent Application Laid-Open No. S62-230638